The present invention relates to compounds that are active as accelerators for curable epoxy and polyurethane systems. The invention relates especially to new compounds that are obtained as reaction products of Mannich bases described hereinbelow with selected amines by means of transamination and that can be used as accelerators in curable epoxy and polyurethane systems.
Numerous curable epoxy systems are known. For certain applications, however, those systems have the disadvantage that they cure too slowly at comparatively low temperatures, that is to say at 5xc2x0 C. or lower. When the atmospheric humidity is, at the same time, relatively high, this results, for example, in coatings or films of inadequate quality being obtained, for example with respect to flexibility, odour, gloss or tackiness. It has now been found that the new compounds according to the invention described hereinbelow are excellently suitable for use as accelerators in curable epoxy and polyurethane systems, the curing rate of the mentioned systems at low temperatures down to xe2x88x925xc2x0 C. being increased to such an extent that the described disadvantageous influence of high atmospheric humidity is substantially or completely overcome. The compounds according to the invention also have the advantage that they are of low molecular weight and comparatively low viscosity. They are therefore readily miscible with the compounds of the curable systems and positively influence the properties of the cured systems. The accelerators according to the invention are, moreover, chemically bonded in the cured systems, which means that the compounds according to the invention can be used in significantly higher concentrations. That is of fundamental importance at low temperatures ( less than 5xc2x0 C.) and currently cannot be achieved with known accelerators, which are not incorporated in the crosslinked network and render the network unusable at relatively high concentrations.
The present invention is defined in the patent claims. The present invention relates especially to compounds that are active as accelerators for curable epoxy and polyurethane systems, characterised in that the compounds are prepared by means of a transamination reaction by reacting
(a) a substituted phenolic compound (Mannich base) having at least one substituent of formula
R1(R2)Nxe2x80x94CH(R3)xe2x80x94xe2x80x83xe2x80x83(A),
xe2x80x83wherein R1 and R2 are each independently of the other linear or branched C1-C4alkyl and R3 is hydrogen, methyl, ethyl or phenyl, with
(b) a compound of formula
R4(R5)Nxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)qxe2x80x94NH2xe2x80x83xe2x80x83(B),
xe2x80x83wherein R4 and R5 are each independently of the other C1-6alkyl or together form a radical of formula xe2x80x94(CH2)5xe2x80x94 or xe2x80x94(CH2)2xe2x80x94Oxe2x80x94(CH2)2xe2x80x94, n is an integer from 2 to 5 and q is zero, 1, 2 or 3, and the compound obtained or the compounds present in the mixture obtained has/have on average, per molecule, at least one substituent of formula
(R4)(R5)Nxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)qxe2x80x94NHxe2x80x94CH(R3)xe2x80x94,
xe2x80x83wherein the substituents R3, R4, R5, n and q have the meanings given above.
The present invention relates also to a process for the preparation of the compounds of the invention, which are active as accelerators, which process is characterised in that, by means of a transamination reaction, (a) a substituted phenolic compound (Mannich base) having at least one substituent of formula
R1(R2)Nxe2x80x94CH(R3)xe2x80x94xe2x80x83xe2x80x83(A)
is so reacted with (b) a compound of formula
R4(R5)Nxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)qxe2x80x94NH2xe2x80x83xe2x80x83(B),
wherein R1, R2, R3, R4, R5, n and q have the meanings given above, that the compound obtained or the compounds present in the mixture obtained has/have on average, per molecule, at least one substituent of formula
(R4)(R5)Nxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)qxe2x80x94NHxe2x80x94CH(R3)xe2x80x94,
wherein the substituents R3, R4, R5, n and q have the meanings given above.
The present invention relates also to the use of the compounds according to the invention as accelerators in curable systems, especially in curable epoxy and polyurethane systems.
The present invention relates also to curable systems, especially curable epoxy and polyurethane systems, comprising a compound according to the invention or a mixture of such compounds, and also to the cured products produced therefrom.
The substituted phenolic compounds (Mannich bases) are preferably low-molecular-weight-di-alkylaminomethyl-substituted phenols, ortho-, meta- and para-cresols, the isomeric xylenols, para-tert-butylphenol, para-nonylphenol, xcex1-naphthol, xcex2-naphthol, diphenols or polyphenols, preferably resorcinol, hydroquinone, 4,4xe2x80x2-dihydroxydiphenyl, 4,4xe2x80x2-dihydroxydiphenyl ether, 4,4xe2x80x2-dihydroxydiphenylsulfone, 4,4xe2x80x2-dihydroxydiphenylmethane, bisphenol A, and the condensation products of phenol and formaldehyde termed novolaks. Preference is given to di-C1-C4alkylaminomethyl-substituted phenols and cresols, especially substituted phenol.
Preferably, R1 and R2 are each independently of the other methyl or ethyl; R1 and R2 are preferably methyl. R3 is preferably hydrogen, methyl or ethyl, preferably hydrogen.
The substituent (A) is preferably di-C1-C4alkylaminomethyl, especially dimethylaminomethyl, ethylmethylaminomethyl and diethylaminomethyl, especially dimethylaminomethyl. The decisive criterion is that it should be possible for the low-molecular-weight dialkylamine liberated in the transamination reaction to be readily removed, by virtue of its low boiling point, from the reaction mixture.
The substituted phenolic compounds are so-called Mannich bases. They are obtained in a manner known per se by reacting the phenolic compound with formaldehyde, acetaldehyde, propionaldehyde or benzaldehyde and the appropriate amine.
Mannich bases preferably used are substituted phenols of formulae (I), (IIa), (IIb) and (III), with preference being given to compounds of formulae (IIa) and (III). In practice, a mixture of those compounds may also be used. The radicals R1 and R2 are as defined for formula (A). 
The substituted phenolic compounds mentioned hereinabove are derived in analogous manner to the phenols of formulae (I), (IIa), (IIb) and (III) mentioned by way of example.
In accordance with the invention, the Mannich bases described above are reacted, by means of a transamination reaction, with compounds of formula (B)
R4(R5)Nxe2x80x94CnH2nxe2x80x94(NHxe2x80x94CnH2n)qxe2x80x94NH2xe2x80x83xe2x80x83(B).
Preferably, R4 and R5 therein are each independently of the other C1-4alkyl, preferably methyl or ethyl. R4 and R5 are preferably methyl. n is preferably 2, 3 or 4, preferably 3. q is preferably zero or 1, preferably zero.
In accordance with the preferred meanings, the corresponding reaction products are also obtained in the transamination reaction.
For example, reaction of the compound of formula (III) with dimethylaminopropylamine results in the following Reaction Scheme 1, wherein H2NR is dimethylaminopropylamine and DMA is the leaving group dimethylamine.
Scheme 1
By means of transamination, only one dimethylaminomethyl substituent or only two of the substituents, of which there are at most three, may, as desired, be brought to reaction, the unreacted dimethylaminomethyl substituent(s) remaining unchanged on the phenolic nucleus. The above Scheme 1 also shows (bottom row) that, on continuation of the reaction, dimerisation and further reaction to linear and branched oligomeric forms occur. Scheme 2 shows the general structure of the oligomeric forms that are then formed.
Scheme 2
In the above compound of formula (IV), xe2x80x94(CH2)sxe2x80x94 corresponds to the radical xe2x80x94CnH2nxe2x80x94 as defined for the compound of formula B.
As will be seen from Scheme 1 and Scheme 2, R6 may be hydrogen, a radical xe2x80x94(CH2)Sxe2x80x94N(R4)R5 or an oligomeric radical.
Reaction of the Mannich bases of formulae (I), (IIa) and (III) with dimethylaminopropylamine, results, for example, in the following monomeric compounds of formulae (V), (VI), (VII), (VIII), (IX) and (X), amongst others, depending on the starting material: 
The compounds of formulae V), (VI), (VII), (VIII), (IX) and (X) are new and the present invention relates thereto. When starting from compounds of formula (IIb), the corresponding 2,4-substituted products are formed under the transamination conditions present.
The transamination reaction is preferably carried out using a compound of formula (IIa), (IIb) or (III) or a mixture of those compounds, together with a compound of formula (B), preferably dimethylaminopropylamine. Depending on the starting material used, there is obtained a corresponding mixture of the compounds of formulae (V) to (X) and corresponding oligomeric compounds, as described above. According to the invention, transamination is carried out until on average, per molecule of the Mannich base, at least one substituent has reacted with the compound of formula (B) so that as few oligomeric compounds as possible form. The transamination reaction is preferably carried out until at least 10% and a maximum of 100%, preferably at least 20% and a maximum of 80%, preferably from 50% to 80%, of the di-C1-C4alkylamino substituents present have reacted with the compound of formula (B). The degree of reaction is measured, for example, by measuring the amine liberated by the Mannich base. An optimum balance between monomeric and oligomeric compounds is generally achieved at a degree of reaction in the range from 60% to 75% of the di-C1-C4alkylamino substituents. This balance also manifests itself on measurement of the viscosity of the composition obtained, the viscosity thereof being preferably in the range from 0.1 Paxc2x7s to 100 Paxc2x7s (25xc2x0 C.), preferably in the range from 1 Paxc2x7s to 30 Paxc2x7s (25xc2x0 C.). The viscosity is preferably  less than 10 Paxc2x7s (25xc2x0 C.).
When the Mannich base of formula (I) is used as starting material, the transamination reaction is carried out until practically all dialkylamino substituents or dimethylamino substituents present have reacted with the compound of formula (B).
The reactants are combined in the reactor preferably in the absence of solvents and are heated to a temperature of from 50 to 150xc2x0 C., preferably from 100 to 130xc2x0 C. The reaction is monitored by determination of the dialkylamine compound split off. At the desired (partial) conversion stage, the reaction is halted by lowering the temperature to about room temperature. The product mixture thereby obtained has shown itself to be storage-stable. Where appropriate, unreacted starting amine (formula B) can be removed by distillation.
In accordance with the invention, the compounds of the invention, which are active as accelerators, are used in curable systems, especially in curable epoxy and polyurethane systems. In principle, the compounds of the invention can be used in the curable systems as hardeners (instead of the hardener customarily used). It is, however, advantageous, in the systems known per se, to use a mixture of the hardener customarily used and the accelerator according to the invention, using preferably from 0.5% to 20%, preferably from 1% to 10% and especially about 5% of accelerator according to the invention (based on the total weight of the hardener customarily used and the accelerator according to the invention).
Epoxy resins that are suitable for use in the curable mixtures are the epoxy resins that are customary in epoxy resin technology. Examples of epoxy resins are:
I) Polyglycidyl and poly-(xcex2-methylglycidyl) esters, obtainable by reacting a compound having at least two carboxyl groups in the molecule and epichlorohydrin or xcex2-methylepichlorohydrin, respectively. Aliphatic polycarboxylic acids may be used as the compound having at least two carboxyl groups in the molecule. Examples of such polycarboxylic acids are oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, sebacic acid, suberic acid, azelaic acid or dimerised or trimerised linoleic acid. Cycloaliphatic polycarboxylic acids may also be used, for example tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid. Aromatic polycarboxylic acids may also be used, for example phthalic acid, isophthalic acid or terephthalic acid. Preference is given to reaction products of acids having two carboxyl groups in the molecule with epichlorohydrin and/or xcex2-methylepichlorohydrin.
II) Polyglycidyl or poly-(xcex2-methylglycidyl) ethers, obtainable by reacting a compound having at least two free alcoholic hydroxy groups and/or phenolic hydroxy groups under alkaline conditions, or in the presence of an acid catalyst and subsequent treatment with an alkali. The glycidyl ethers of this kind are derived, for example, from acyclic alcohols, e.g. ethylene glycol, diethylene glycol and higher poly(oxyethylene) glycols, propane-1,2-diol or poly(oxypropylene) glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol, sorbitol and also from polyepichlorohydrins. They are, however, also derived, for example, from cycloaliphatic alcohols, e.g. 1,4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane, or they have aromatic nuclei, e.g. N,N-bis(2-hydroxyethyl)aniline or p,pxe2x80x2-bis(2-hydroxyethylamino)diphenylmethane. The glycidyl ethers can also be derived from mononuclear phenols, e.g. resorcinol or hydroquinone, or they are based on polynuclear phenols, such as bis(4-hydroxyphenyl)methane, 4,4xe2x80x2-dihydroxybiphenyl, bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane and on novolaks, obtainable by condensation of aldehydes, e.g. formaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols, e.g. phenol, or with phenols substituted on the nucleus by chlorine atoms or C1-C9alkyl groups, e.g. 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol, or by condensation with bisphenols such as those of the kind mentioned above. Preference is given to reaction products of compounds having two free alcoholic hydroxy groups and/or phenolic hydroxy groups with epichlorohydrin and/or xcex2-methylepichlorohydrin.
III) Poly(N-glycidyl) compounds, obtainable by dehydrochlorination of the reaction products of epichlorohydrin with amines containing at least two amine hydrogen atoms. Such amines are, for example, aniline, n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine or bis(4-methylaminophenyl)methane. The poly(N-glycidyl) compounds also include, however, triglycidyl isocyanurate, N,Nxe2x80x2-diglycidyl derivatives of cycloalkylene ureas, e.g. ethylene urea or 1,3-propylene urea, and diglycidyl derivatives of hydantoins, e.g. 5,5-dimethylhydantoin. Preference is given to reaction products of amines containing two reactive amine hydrogen atoms with epichlorohydrin and/or xcex2-methylepichlorohydrin.
IV) Poly(S-glycidyl) compounds, such as di-S-glycidyl derivatives which are derived from dithiols, e.g. ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.
V) Cycloaliphatic epoxy resins, e.g. bis(2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentylglycidyl ether, 1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxycyclohexylmethyl 3xe2x80x2,4xe2x80x2-epoxycyclohexanecarboxylate.
It is also possible, however, to use epoxy resins wherein the 1,2-epoxide groups are bound to different hetero atoms or functional groups; such compounds include, for example, the N,N,O-triglycidyl derivative of 4-aminophenol, the glycidyl ether-glycidyl ester of salicylic acid, N-glycidyl-Nxe2x80x2-(2-glycidyloxypropyl)-5,5-dimethylhydantoin and 2-glycidyloxy-1,3-bis(5,5-dimethyl-l-glycidylhydantoin-3-yl)propane, preference being given in each case to compounds containing two epoxide groups.
In the curable mixtures according to the invention, a liquid or viscous polyglycidyl ether or ester is preferably used as the epoxy resin.
Preference is given to the mentioned aromatic and/or aliphatic polyglycidyl ethers that are suitable for low-temperature curing ( less than 5xc2x0 C.).
The epoxy compounds used as starting material are known per se and, in some cases, commercially available. Mixtures of epoxy resins may also be used. All customary hardeners for epoxides may be used, for example amines, carboxylic acids, carboxylic acid anhydrides or phenols. Moreover, catalytic hardeners, for example imidazoles, may also be used. Such hardeners are described, for example, in H. Lee, K. Neville, Handbook of Epoxy Resins, McGraw Hill Book Company, 1967, pages 10-17. Preferred hardeners are polyamino compounds known per se, special preference being given to aliphatic polyamino compounds, for example isophorone-diamine or diethylenetriamine, and the higher-molecular-weight polyamines known per se.
The amount of curing agent used depends on the chemical nature of the curing agent and the desired properties of the curable mixture and of the cured product. The maximum amount can be readily determined by the person skilled in the art especially on the basis of stoichiometric calculations.
Suitable polyurethane systems for use of the compounds according to the invention are described, for example, in Kunststoff Handbuch [Plastics Handbook] No. 7, xe2x80x9cPolyurethanexe2x80x9d (Verlag Carl Hanser 1983) (chapter 2.2, pages 12-19). The catalysts mentioned therein (chapter 3.41., page 92ff) may be replaced partly or wholly by the accelerators according to the invention.
Preparation of the mixtures comprising epoxy or polyurethane component, hardener and accelerator according to the invention may be carried out in conventional manner by mixing together the components by manually stirring or using known mixing apparatus, for example stirrers, kneaders or rollers. Depending upon the application, customary additives, for example fillers, pigments, dyes, flow improvers or plasticisers, may be added to the mixtures. In a manner known per se, the resins according to the invention may be offered commercially in the form of two-component systems.